Low friction live-loaded packing

ABSTRACT

A valve packing assembly for a control valve includes a seal assembly, a loading assembly, and a packing retainer. The seal assembly has a seal component to provide a fluid seal around a valve stem and an anti-extrusion component to substantially prevent extrusion of the seal component about the valve stem. The loading assembly is configured to advantageously provide a predetermined packing stress to the seal assembly that is in the same direction as a process stress applied to the seal assembly by a process fluid, thereby substantially reducing packing friction and packing wear in the control valve assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional of U.S. patent application Ser. No. 11/841,423,filed Aug. 20, 2007, which claims the benefit of priority of U.S.Provisional Patent Application No. 60/840,369, filed Aug. 25, 2006, theentire contents of which are hereby expressly incorporated herein byreference.

FIELD OF THE INVENTION

disclosure relates generally to packing for valves, and moreparticularly, to an improvement of live-loaded packing for controlvalves used in process control applications that require very lowemission levels from valve packing.

BACKGROUND OF THE INVENTION

In the process control industry, it is known that many processapplications require control valves that leak very small amounts of aprocess fluid into the surrounding environment. In fact, some processplants are subject to federal regulation under the 1990 Amendments tothe Clean Air Act which regulates the amount of certain processemissions, such as aromatic or chlorinated hydrocarbons, based uponmeasured emission concentrations (e.g., less than 500 parts per millionby volume (ppmv)) that leak from control valve assemblies into the plantenvironment. Typical solutions to reduce such emissions include placinga bellows seal around the control valve stem to contain the emissions orinstalling spring-loaded or live-loaded packing assemblies within thecontrol valve body to maintain the emissions at acceptable concentrationlevels during valve operation.

Typical bellows seals create an external, “accordion-like” environmentalseal by attaching a flexible metal chamber (i.e., a bellows) around anexposed portion of the valve stem. The bellows seals are intended tocapture and contain process fluids within the bellows chamber, therebypreventing escape to the surrounding environment. To be functional, thebellows must remain flexible through a large operational temperaturerange and be resistant to various types of corrosion, which generallyrequires the use of special metals. Bellows are generally made fromexpensive alloys such as Inconel® from Special Metals Corporation of NewHartford, N.Y. or Hastelloy® C from Haynes International, Inc. ofKokomo, Ind. Both special metals significantly increase the cost of thebellows seal. Additionally, bellows seals are expensive to install asthe bellows are generally seal-welded to the valve stem, gasket-sealedat the bonnet/valve joint and require an extended valve bonnet. Thephysical construction of the bellows and this installation method alsoplaces limits on the amount of rotation that can occur in the valvestem. In order to prevent damaging the weld or the seal, ananti-rotation device must often be installed to limit the amount ofvalve stem rotation during operation. Bellows seals are also designedfor a specific length of travel to maximize bellows fatigue life.Applications producing travel greater than the designed length of travelmay damage the bellows by extending the “folds” beyond the designedlength causing premature cycle fatigue or cracking to occur. Analternative to capturing the leaking emissions in a bellows seal is toprevent the emissions from occurring using improVed control valvepacking such as live-loaded packing.

Conventional live-loaded packing sets are installed within a packingbore of the control valve assembly to seal around the valve stem tosubstantially reduce emissions from the packing set during operation. Itis generally understood that the packing must be axially loaded orstressed to force radial expansion of the packing components to affect adynamic seal on a moving valve stem and a static seal in the packingbore where the packing components are in contact within the controlvalve body. As used in the present description, it should be understoodby one of ordinary skill in the art that the term packing stress meansan axial force from a loading device, such as a spring, or from processpressure acting on the packing set that is divided by the annular areaof the packing. Furthermore, the packing assemblies described herein useV-ring sealing components (i.e., the cross-section of the packing is inthe shape of a “V”) designed to amplify the axial packing stress into alarger radial contact stress to promote sealing by concentrating theaxial forces in radial directions. It is generally known thatenvironmental, live-loaded packing assemblies have certain limitations.FIG. 1 graphically represents the various types of example packingstress relative to a process packing pressure, A, described in detailbelow. One skilled of ordinary skill in the art should appreciate thatpacking stresses below the process pressure, A, may generally result inprocess fluid leaks since the process pressure may overwhelm a sealformed by the packing stress.

One type of conventional live-loaded packing is termed automaticpacking. A seal is provided by a single V-ring packing set that isaxially loaded by a coil spring that exerts a relatively small packingstress on the packing rings such as Single PTFE packing available fromFisher Controls International LLC of St. Louis, Mo. One skilled in theart understands that this type of packing set uses a V-ring with a highaxial force-to-radial force ratio. That is, the V-ring is constructed toprovide high radial expansion under the relatively low spring rate of acoil spring for a given application. This type of automatic packing istypically rated for environmental service (e.g., <500 ppmvconcentration) at a maximum pressure of 300 psi, as shown in FIG. 1 asaxial packing stress B, and a maximum temperature of 200° F. These typesof packing may be loaded from the inboard or pressure side of thecontrol valve, but are generally only applicable to low pressure,environmental applications due to the coil spring loading.

Another type of packing is generally described as double V-ring packing.This packing assembly uses two low pressure V-ring packing sets similarto the single V-ring packing described above with the packing setsarranged as an upper and a lower seal component, but without any type ofspring loaded device to exert the packing stress. The packing set isstressed under a static packing load to create the valve stem seal witha packing nut/packing follower assembly known to those skilled in theart. The shortcoming of is type of packing is that without a springelement to ensure an adequate level of packing stress over a largetemperature range, the packing design cannot be rated for environmentalservice, and, as such, is not depicted in FIG. 1.

Yet another type of environmental packing is a double V-ring,live-loaded packing set commercially available as Enviro-Seal® PTFEpacking from Fisher Controls International LLC of St. Louis, Mo. Thistype of packing set uses a high pressure V-ring (i.e. a low ratio ofaxial force-to-radial force) loaded by a high-spring rate loading devicesuch as a Belleville spring. In comparison to coil spring loading, theBelleville springs have a much greater spring rate to provide arelatively large force or packing stress required to compress the doubleV-ring packing for high pressure applications. This type of packing istypically rated for environmental service at a maximum pressure of 750psi and a maximum temperature of 450° F. One issue with this type ofpacking assembly relates to the uses of Belleville springs to load thepacking. Although the Belleville springs provide the required packingstress, the travel or range of compression of the Belleville springs isquite low. This combination of high spring rate and low or small travelrange results in the need for very precise initial adjustment of theBelleville spring preload and/or tightly held manufacturing tolerancesto obtain the desired packing stress. That is, one of ordinary skill inthe art should appreciate that the packing stress per unit travel orcompression of the Belleville springs is relatively large. As such,normal manufacturing tolerances within the control valve assemblynecessitate manual adjustment, which can be very difficult and timeconsuming (e.g., the Fisher Controls Design D2 dump valves uses threeBelleville spring stacked in series, which require adjustment precisionwithin ±0.0024 inches to achieve a packing stress within ±50 psi). Thus,if the packing stress is too high, high packing friction may result,which can reduce control valve performance and packing life.

Additionally, coil springs typically are not used with high pressure,double V-ring packing due to the fact that bonnet/packing box area islimited and the cross-sectional area of coil spring needed to developthe proper spring rate will be too large. Furthermore, this type ofpacking set is typically loaded from the outboard side (i.e. external oratmospheric side as compared to the inboard or pressure side) of thecontrol valve providing a packing force that opposes a force produced bythe process pressure. Because the Belleville spring force opposes theforce produced by the process pressure, the spring forces are notadditive to the packing stress; therefore, the initial packing stressrequired to create the environmental seal must be accounted for in theinitial packing setup by increasing the initial packing stress, as shownas a packing stress C of FIG. 1, which is independent of the processpressure until the process pressure matches the packing stress. Thisovercompensation in the initial packing stress creates greater frictionin the assembly, which may cause the control valve actuator to beoversized, thereby adding expense to the control valve and resulting ingreater packing wear during operation.

Another commercially available packing suited for high-temperature,high-pressure environmental service is a graphite-based packing withintegrated PTFE known as Enviro-Seal Graphite ULF from Fisher ControlsInternational LLC of St. Louis, Mo. This type of packing set usesgraphite-based packing rings for high temperature operation with smallamounts of PTFE integrated in seal components to minimize friction.Belleville springs are used to supply the packing stress. Unlike theprevious packing sets, the extremely high axial force-to-radial forceratio of the graphite-based seal rings requires very high spring ratesto create the environmental seal. For this type of packing, theBelleville springs create a very large force from the opposite directionof a force generated by the process pressure resulting in a packingstress that can approximate 4500 psi (shown as constant packing stress Din FIG. 1). Similar to other types of Belleville spring-based packingassemblies, the travel of the Belleville springs is very low requiringvery precise initial adjustments to control the packing stress. Althoughthis type of packing is rated for environmental service at a maximumpressure of 1500 psi and a maximum temperature of 600° F., the frictionlevels produced by this packing arrangement may be substantially higherthan PTFE packing at temperatures below 300° F. and may be unacceptablein certain types of applications (e.g., applications without controlvalve positioners).

Accordingly, it is desired to provide an improved live-loaded packingsystem with improved operating range of performance which can apply auniform stress to the valve stem packing, such that the packing stressremains at a constant level above a process pressure during operation.It is also desired to provide a live-loaded packing system to reducepacking friction for improved control valve performance and reducedpacking wear for improved maintenance.

SUMMARY OF THE INVENTION

In an example packing assembly, a seal assembly comprising a sealcomponent to provide a fluid seal around a valve stem and ananti-extrusion component to substantially prevent extrusion of the sealcomponent about the valve stem and a loading assembly to provide apredetermined packing stress upon the seal assembly to couple thepacking stress between the loading means and the seal assembly. Thepacking assembly further includes a packing retainer adapted to receiveat least one of the seal assembly and loading assembly and is configuredto couple the seal assembly and loading assembly to the control valveassembly. The packing retainer further includes a shoulder to engage apacking box within the control valve assembly to control a loadingassembly preload to provide a predetermined packing stress tosubstantially reduce the packing friction and packing wear in thecontrol valve assembly.

In another example packing assembly, a cartridge packing assemblycomprises a seal assembly having a seal component to provide a fluidseal around the valve stem and, at least, a first anti-extrusioncomponent to substantially prevent extrusion of the seal member aboutthe valve stem and a loading assembly having a loading means to providea predetermined packing stress upon the seal assembly and a followercomponent to couple the loading means to the seal assembly. The packingassembly further comprises a packing retainer adapted to be disposed ina packing box of the control valve assembly to receive the seal assemblyand the loading assembly and having a shoulder to engage the controlvalve assembly to control the preload of the loading assembly to providea predetermined packing stress to substantially reduce the packingfriction and packing wear in the control valve assembly. The examplepacking retainer further includes an adjustment means to modify thepacking stress upon installation.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of this invention which are believed to be novel are setforth with particularity in the appended claims. The invention may hebest understood by reference to the following description taken inconjunction with the accompanying drawings wherein like referencenumerals identify like elements in the several figures, in which:

FIG. 1 is a graphical representation of the process pressure versusaxial packing stress for various types of packing assemblies;

FIG. 2 is a split partial cross-sectional view of a live-loaded packingassembly in accordance with an example packing set;

FIG. 3 is a split partial cross-sectional view of a live-loadedcartridge packing assembly in accordance with an example packing set;

FIG. 4 is a split partial cross-sectional view of a live-loadedcartridge packing assembly in accordance with an example packing set.

DETAILED DESCRIPTION

The example packing assembly uses a stack of seal rings andanti-extrusion rings to provide a high-pressure fluid seal assemblyaround a control valve shaft. The seal assembly may be characterized asfollows: 1) a loading assembly, such as a Belleville spring stack, thatprovides compliant packing stress with sufficient travel to provideimproved adjustments in packing wherein the packing stress is exerted inthe same direction as a fluid pressure exerted by the process fluid; 2)a packing retainer arranged to engage a control valve body or bonnetassembly to substantially eliminate the need to initially adjust thepacking stress to overcome or offset the process pressure therebyproviding an environmental seal with reduced friction and reducedpacking set wear; 3) a seal assembly with anti-extrusion washers andrings that substantially reduces valve shaft and/or seal wear duringoperation; and 4) a cartridge seal assembly that substantially improvesthe repair or replacement of the packing assembly. The improved packingassembly provides a cost-effective means to provide packing stress that“tracks” the process pressure by providing a constant packing stressthat is above a packing stress which results from a process pressure toallow the packing to operate at the lowest acceptable stress, therebyminimizing friction and maximizing packing life. Tracking the processpressure will be described in greater detail below.

In a first example packing assembly illustrated in FIG. 2, asplit-partial, cross-section shows the packing assembly 100 unloaded orunstressed in the left half-plane, and loaded or stressed in the righthalf-plane. It should be understood by one of ordinary skill in the artthat, by way of the example, the packing assembly described hereinrelative to a bonnet assembly 190; however, this description is notintended to limit the example packing assembly to such specificapplications. For example, the example packing assembly could beinstalled directly into a packing box within a control valve or anactuator assembly without departing from the spirit and scope of theinvention.

As previously described, many control valve applications require anenvironmental seal around a valve stem to prevent leaks of process fluidinto the surrounding atmosphere. Additionally, many conventional packingsets are installed from the outboard side of the control valve (i.e.,the top side or atmospheric pressure side external of the control valvebody) and are generally loaded or stressed from the outboard side. Thistype of packing configuration is stressed by a force in opposition tothe force generated by a process pressure that often results in initialpacking stresses exceeding an amount required to create theenvironmental seal, which can degrade control valve performance, asdescribed below.

In the present example, a packing assembly 100 to provide anenvironmental fluid seal is shown installed in a bonnet assembly 190 asan inboard-installed (i.e., installed relative to the inboard side orpressure side of the control valve body), bottom-loaded packingassembly. Specifically, the packing assembly 100 is positioned within apacking box 180 of the bonnet assembly 190 and receives a valve stem 115via a throughbore 136 that extends through the packing assembly 100 andinto the inboard side of the control valve which connects to a fluidcontrol device (not shown) such as a valve plug to control the flow afluid through the control valve. The packing box 180 of the bonnetassembly 190 is comprised of three substantially concentric bores 137,138 and 139 to accommodate the valve stem 115 and the packing assembly100. A first bore is an outer clearance bore 137 for the valve stem 115to permit movement along an axial direction, Z, to couple the desiredvalve stem motion to the valve plug to control fluid flow within avalve. By providing a valve stem clearance contact is avoided to thevalve stem 115, which may result in leaks by moving the damaged portionof the stem through the packing assembly 120. A second bore within thebonnet assembly 190 is a packing bore 138 provided to house a packingset 120 that provides the sealing mechanism of the packing assembly 100.The packing bore 138 is defined by a wall 142 that terminates in apacking bore shoulder 143 on the outboard side of the bonnet assembly190 to provide a seating surface for the packing set 120. A third bore,relatively larger than the outer clearance bore 137 and the packing bore138, is a retainer bore 139 configured to engage a packing retainer 155to provide a pre-adjusted packing stress, as explained in greater detailbelow.

The packing set 120 is comprised of a single seal ring 125 and twoanti-extrusion rings 123 and 127 commonly referred to as a V-ring typepacking set. As shown in FIG. 2, the example packing set 120 includes anupper female adapter ring 123; a middle seal ring 125; and a lower maleadapter ring 127 placed in intimate contact around the circumference ofthe valve stem 115. One skilled in the art can appreciate that variouscombinations of V-rings could also be used to achieve an environmentalseal (e.g. five or seven V-ring sets). The V-ring type packing rings123, 125 and 127 may be formed of polytetrafluoroethylene (PTFE), knownas a V-type PTFE packing available from the John H. Crane Company ofMorton Grove, Ill. Packing suitably formed of other material, or ofother synthetic resin polymers, may also be used. Additionally, theadapter rings 123 and 127 may he carbon filled to provide greaterrigidity under load which may create an improved seal, as describedbelow.

The V-ring packing is preferred because under axial packing stress theV-shape cross-section inherently creates a radial load expanding thepacking set to create an improved seal. In other words, under a load,the V-rings 123, 125 and 127 are axially compressed, which forces anassociated radial expansion of the middle seal ring 125 both into thevalve stem 115 and into the packing bore 138 as the mating V-shapedsurfaces are driven into each other. Preferably, as each adapter ring123 and 127 is relatively less compliant than the middle seal ring 125,thereby concentrating the packing stress in the middle ring to providethe fluid seal.

At elevated temperatures and/or elevated pressures, PTFE V-ring packingrings may extrude (i.e., distort from the original shape along a pathwaysuch as the clearance bore 136 away from the seal ring 125) resulting ina loss of contained packing volume. The “translocation” of the packingmay produce a subsequent loss of packing volume within the packing setyielding a reduction in associated packing stress, which may cause thepacking to leak. To prevent such extrusion, the packing assembly usestwo anti-extrusion washers 132 and 133 positioned on an outboard andinboard side of the packing set 120, as shown in FIG. 2. Bothanti-extrusion washers 132 and 133 are characterized as generallynon-compressible (e.g., the washers do not substantially compress in anaxial direction nor expand in a radial direction) under the packingstress exerted to form the fluid seal.

Accordingly, the upper anti-extrusion washer 132 mates to the packingbore shoulder 143 to prevent extrusion through the clearance bore 136 onthe outboard side of the valve body and the lower anti-extrusion washer133 mates to a spacer 141 to prevent extrusion past the spacer 141towards the inboard side of the valve stem 115. Both anti-extrusionrings also make contact with the packing bore wall 142 to contain theseal ring within the packing bore 138. One skilled in the art shouldalso appreciate that the lower anti-extrusion washer 133 may be removedfrom the packing set 120 without substantially degrading anti-extrusionperformance of the packing set 120. That is, it is believed thatbottom-loading of the packing set, as described below, in addition to anoutboard-directed force provided by the process pressure (shown asvector P in FIG. 2), may produce extrusion only to the outboard side ofthe bonnet assembly 190.

Each anti-extrusion washer is formed of a composition material, one offilled-PTFE having filler selected from at least one of the following:graphite, carbon, silica or of barium sulfate that is commerciallyavailable as Gylon® from Garlock Sealing Technologies of Palmyra, N.Y.The anti-extrusion washers are generally formed of a material that issufficiently hard, relative to the packing rings, to prevent extrusion.It has been observed that a common anti-extrusion washer material, suchthe Gylong® 3510 material, may cause valve stem wear in certainhigh-cycle control valve applications (e.g., applications accumulating alarge number of cycles such as 25,000 cycles).

Gylon 3510 is understood to be a composite material made from PTFEcontaining the mineral barium sulfate (i.e. substantially the mineralbarite). In high-cycle applications, the barium sulfate may actuallycause microscopic stem wear which can degrade packing performance.Barium sulfate is known to have a hardness of approximately 3 on theMobs (HM) hardness scale, which is approximately 19 on the Rockwell Chardness scale (HRC). Valve stems are commonly made from S31600 which isknown to have a hardness of approximately 25 HRC. It is believed thatthe mineral filler may have sufficient hardness to induce gradual wearor abrasion on the stem, which may cause packing degradation inoperation. This may be because the anti-extrusion washers aresubstantially adjacent to the PTFE packing seal rings such that stemabrasion caused by the anti-extrusion washers will be positioned to makefrequent contact with the PTFE packing ring during stroking of thevalve, thereby causing roughened surfaces on the sealing portion of thestem. The abraded surfaces increase the wear rate of the packing sealrings which may produce undesirable leaks that require maintenance andrepair.

Conversely, if this abrasion can be substantially decreased, the usefullife of the packing assembly could be substantially increased. In thepresent example packing assembly, each anti-extrusion ring is preferablyformed of a composite material of filled-PTFE having filler molybdenumdisulfide and polyetheretherketone (PEEK) reinforcing polymer known asTCM® Ultra available from Fisher Controls International. Additionalreference to the composite material may be made to the seal materialdescribed in U.S. Pat. No. 5,823,540, assigned to the present assignee,and hereby expressly incorporated by reference. The substantially lessabrasive TCM Ultra filler material (i.e., molybdenum disulfide hardnessis approximately 1 HM) is expected to increase the cycle life of examplepacking assembly and may also extend temperature range fromapproximately 450° F. to 500° F. Additionally, anti-extrusion rings madefrom TCM Ultra may be formed from a conventional molding process whichis substantially less expensive than the die-cut stamping process usedto make the typical Gylon 3510 parts.

As previously discussed, to form a fluid seal, the seal ring 125 must beradially expanded into the valve stem 115 and the packing bore 138. Inthe example packing assembly 100, the axial packing stress istransmitted through the substantially non-compressible spacer 141 from aloading assembly 140. The spacer 141 is generally made of S31600 andmakes intimate contact with the wall 142 of the packing bore 138. Aclearance bore is provided to receive the valve stem 115 withoutabrading the stem surface and to prolong packing life. The axial packingstress is generated from a loading force (shown as vector L in FIG. 2) bthe loading assembly 140 of the example packing assembly 100. Theloading assembly 140 is preferably comprised of a stack of Bellevillesprings, but one of ordinary skill in the art understands that otherspring devices may be contemplated provided that the spring device cansupply an appropriate amount of predetermined packing stress over thedesired travel range. For example, a coil spring may be used, but thegenerally lower spring rate from a coil spring may require asignificantly larger packing box volume to accommodate the assembly,which can increase control valve cost and create mounting andinstallation problems.

Unlike conventional Belleville springs, the loading assembly 140 of theexample packing assembly 100 uses Belleville disk springs that have arelatively lower spring rate and longer travel or compression, asdescribed in greater detail below. The loading assembly 140 is retainedand compressed by a packing retainer 155 which is configured to beattached to the control valve body (not shown) from the inboard side.The packing retainer 155 is formed in a generally cylindrical shapehaving a substantially cylindrical cavity forming a loading assemblybore 165 for receiving the loading assembly 140 and second retainer bore170 for receiving the valve stem 115 and/or a journal bearing 175. Incertain applications, the journal bearing may provide guiding of thevalve stem 115 through the packing assembly 100. To retain the journalbearing, the journal bearing 175 may include an engagement lip 182formed to a engage a chamfered edge 183 of the packing retainer 155 andbeing held in position by compression of the Belleville springs of theloading assembly 140.

One such configuration to compress the loading assembly 140 is shownFIG. 2 of the example embodiment with external mating threads 185 thatengage a corresponding thread 151 in a portion of the retainer bore 139.One skilled in the art should appreciate that other methods may becontemplated such as a clamped in design. Alternatively, in applicationswhere valve stem guiding is not required, the journal bearing may beremoved and the valve stem 115 passes through the clearance bore 170without making any contact, thereby preserving the surface finish of thevalve stem 115. One skilled in the art should appreciate that theinstallation and retaining mechanism of the example packing assembly maysignificantly reduce the installation and adjustment of the packingassembly.

Conventional live-loaded packing assemblies generally have what is knownas a tolerance stack-up issue. This occurs when the packing assemblycomponents and the control valve body overwhelm the travel orcompression of the Belleville spring stack such that the adjustments ofthe packing assembly pre-load must be precisely set, as previouslyexplained. Generally, this requires an operator to install the packingset within the control valve body or bonnet assembly and subsequentlytighten the packing until the adjustment “bottoms out” (i.e., there isno adjustment remaining). The operator must subsequently loosen thepacking assembly adjustment mechanism a precise number of rotations,depending upon the application, to set the packing at the desired stresslevel.

To avoid this issue, the example retainer 155 includes a retainershoulder 168 as shown that contacts a retainer bore mating surface 166when the retainer 155 is threaded into the retainer bore 139 of thebonnet assembly 190 to pre-set the packing stress. That is, theretaining shoulder 168 and the sizing of the loading assembly bore 165are predetermined to precisely pre-load the packing assembly 120 whenthe retainer 155 is tightly threaded in to the bonnet assembly 190. Forexample, in the present example packing assembly 100 uses controlleddimensions to set the stress and five longer travel Belleville springsto increase the manufacturing tolerance stack-can be up to ±0.015inches. Additionally the packing retainer 155 may have an externalsurface 178 formed to accept a standard socket, such as a hexagonalcross-section, to provide a convenient method to tighten the retainer155 into the bonnet assembly 190.

It should be appreciated by one of ordinary skill in the art that thelower spring rates may be derived from the thinner Belleville disksprings. Thus, even though the Belleville springs have a relativelylower spring rate when compared to conventional packing assemblies, thelonger travel range in combination with the lower spring rate providesadequate packing stress under a predetermined compression or load toprovide an environmental seal with minimal friction. For example, in thepresent bottom-loaded packing assembly 100, a Belleville spring stackthat can supply a packing stress of approximately 450 psi may result inan environmental seal in a valve such as the Fisher Controls Design D2.Thus, when the packing is tightened, the packing retainer bottoms out ona mating surface in the bonnet assembly creating the desired amount ofinitial packing stress. More significant, due to the bottom-loadedassembly, as the process pressure increases, the packing stress of theexample bottom-loaded packing stays above the process pressure by anamount equal to the initial packing stress (i.e., the loading assemblyforce is not in opposition to the force created by the processpressure). With this design, the initial packing stress can be selectedto give the desired performance characteristics for the application.

As an example, to create an environmental seal with the present examplepacking assembly that has 1500 psi packing stress under 750 psi processconditions only 750 psi of packing stress is required. This is asignificant decrease in packing stress as compared to conventionaldouble V-ring, live-loaded packing, 1500 psi packing stress, which mayrequire an initial packing stress of 1500 psi. In other words, thebottom-loaded packing assembly 100 provides a packing stress that allowsfor a constant packing stress above the stress provided by theprevailing process conditions. That is, the packing stress of theexample packing assembl “tracks” the process pressure with a packingstress-margin that is substantially equal to the initial packing stressand is constantly present such that the minimum packing stress will besubstantially equal to the initial packing stress, as shown in FIG. 1 aspacking stress E.

Alternatively, in process applications producing process pressures of1000 psi, the example packing assembly 100 may use an initial packingstress of 500 psi to achieve a 1500 psi packing stress for anenvironmental seal. The lower packing stress of the example packingassembly 100 may reduce packing wear and packing friction to improveoverall control valve performance and reduce maintenance expenses. Itshould be noted and appreciated by one of ordinary skill in the art thatthe example packing set will maintain an adequate environmental sealwhen operated in a vacuum service. That is, the initial packing stresscan be set such that the under operating conditions drawing a vacuum(e.g., −14.7 psi) the pressure conditions are a relatively insubstantialpercentage of the total packing stress exerted upon the packingassembly.

An alternate example packing assembly is illustrated in FIG. 3. Thistype packing assembly may be installed in the body of a control valve,such as a conventional sliding stem globe valve, and may be defined asan outboard-installed, bottom-loaded packing assembly. That is, thepacking assembly may be installed from the external side of the controlvalve and, as such, is suitable for either new installation or repairapplications. Additionally, the split-partial cross-sectional viewillustrated in FIG. 3 shows a non-adjustable cartridge packing assemblyin the left-half plane and an adjustable cartridge packing assembly inthe right-half plane. Similar elements have been given like referencenumerals. The cartridge packing assembly 200 is similar to the previousexample packing assembly in that it includes an assembly throughbore 236that receives a valve stem 215 which connects to an inboard valve plug(not shown) to control fluid through the control valve.

The example cartridge packing assembly 200 is installed in a packing box280 on the outboard side of a control valve body 290 and is comprised oftwo substantially concentric bores as shown. The first bore is a packingbore 238 which houses the cartridge packing assembly 200 and iscomprised of inner wall 239 terminating in a chamfered-edge shoulder 286that generally separates the main fluid flow path (not shown) in thepressure side of the control valve from the packing bore 238. The secondbore is a clearance bore 270 for the valve stem 215 to permit valvestern 215 to move along a longitudinal axis, Z, clearance between thevalve stem and the walls of the second bore is provided to prevent stemabrasion. The cartridge packing assembly 200 is retained within thepacking box 280 by a packing flange 228 having a generally T-shapedcross-section that provides a flange mating surface 272 to attach to thecontrol valve on an upper surface 273.

In the non-adjustable cartridge packing assembly shown in the left-halfplane of FIG. 3, the packing flange 228 includes a lower substantiallycylindrical portion 229 and has a first bore 236 for placing the valvestem 215 therethrough as shown. A clearance hole is provided about thevalve stem 215 to substantially eliminate stem abrasion from the packingflange 228. A packing retainer 255 is positioned within the packing box280 and is adapted to receive the lower portion 229 of the packingflange 228 within a packing bore 242 to provide a controlled surfacedimension. This surface dimension will be used to compress a packing set220 to produce a predetermined packing stress and will be described ingreater detail below. As shown, the packing flange 228 attaches to thecontrol valve body 290 with fasteners 275 that pass through clearanceholes 274 and engage an internal threaded portion 276 of the valve body290. Other methods may be employed such as clamping methods know tothose skilled in the art. The sealing components of the examplecartridge packing assembly 200 are similar to the previously describedinboard-installed packing assembly.

As shown in FIG. 3, the packing set 220 is comprised of a single sealring 225 and two anti-extrusion rings 223 and 227. The materials ofconstruction are substantially similar to those previously described forlike components. Additionally, to prevent extrusion, the packingassembly 220 also uses two anti-extrusion washers 232 and 233 positionedon an outboard and inboard side of the packing set 220, as shown in FIG.3. As previously discussed, to form a fluid seal the seal ring 225 mustbe radially expanded into the valve stem 215 and the packing bore 238.In the example packing assembly 200, an axial loading force istransmitted through the substantially non-compressible spacer 241 from aloading assembly 240, preferably comprised of a stack of Bellevillesprings as previously described. One skilled in the art shouldappreciate that the present example packing assembly 200 may alsoinclude a journal bearing (not shown) a guide sleeve disposed in theclearance bore 270 to substantially reduce the effects of any side loadsexerted by turbulent process fluids or actuator misalignment.

For the non-adjustable arrangement shown on the left-half plane of FIG.3, it should be understood by one of ordinary skill in the art, that apre-determined packing stress is established by a controlled distancebetween a top surface of a retainer shoulder 268 and a seating surface265 for the loading assembly 240 and the length of cylinder portion 229of the flange 228 with respect to the flange mating surface 272. Aspreviously explained, conventional live-loaded packing assembliesgenerally have a tolerance stack-up within the control valve assemblycomponents that can overwhelm the travel or compression of theBelleville spring stack.

Quite the opposite, the example packing set 200 provides a tolerancestack-up with respect to only two controlled dimensions. As such, thecontrolled distance between the retainer shoulder 268; the seat surface265; and the cylindrical portion 229 of the flange 228 ensures accurateBelleville spring load. In other words, the load is determined bycontrolling the packing box depth within the sleeve rather than thedepth of the original valve bore. Further, the example packing assembly200 in the left-half plane substantially improves the repair orreconditioning process for existing valves by returning the packing boxbore to new condition by “sleeving” the old bore with the new retainer255. The new retainer 255 may provide improved corrosion resistancebeing made from a corrosion resistance metal or alloy such as S31600 orsimilar corrosion resistant, thermally stable polymers including PEEK.In fact, the packing retainer 255 may be used in a packing box 280wherein the packing box may be over-bored or otherwised damaged by usinga seal component such as an o-ring 293 or the like, positioned within anannual recess 294, to effectively seal between the packing retainer 255and the packing bore 238. Alternatively, the split-partial cross-sectionview illustrated in right-half plane of FIG. 3 shows an adjustablecartridge packing assembly in the right-half plane as described below.That is, in certain applications, adjustments of the packing stress maybe desirable (e.g., worn packing sets that require additional packingstress to ensure an environmental seal).

By accurately controlling the Belleville spring compression, and therebyaccurately controlling the packing stress, packing performance can besignificantly improved and variability can be significantly reducedcompared to traditional externally adjusted packing. However, based uponthe initial installation, after the packing has reached the end of itsuseful life, there is also the need to address packing leaks caused byworn packing. Typically, the packing must be tightened to stop packingleakage until maintenance can be scheduled to replace the packing set.This can be accomplished by a non-sealed adjustment screw 291 thatengages with the retainer 255 to move the packing set 220 along an axialdirection. It should be appreciated by one of ordinary skill in the artthat the adjustment screw 291 does not need to be sealed because theadjustment means is external to the fluid seal created by the packingassembly 220. The adjustment screw 291 an additional mechanism to setthe packing stress to a desired stress greater than that determined bythe pre-determined length of engagement of the lower cylinder portion229 of the packing flange 228, similar to the non-adjustable packingassembly previously described. That is, a supplemental spacer 241positioned on the outboard side of the packing set 220 may be driventowards the packing set 220 to further compress the sealing ring 225 andincrease the packing stress.

Additionally, one of ordinary skill in the art may also appreciate thatan annular spanner ring (not shown) could also he used to adjust and seta packing stress. One should also appreciate that the adjustment screwcan be designed to travel more than the Belleville springs, givingmaintenance personnel the ability to apply very high packing stress ifrequired. For example, such stress may be necessary to sufficientlyreduce the leakage of severely worn packing.

An alternate example cartridge packing assembly is illustrated in FIG.4. This type cartridge packing assembly may be also installed in thebody of a control valve, such as a conventional sliding stem globevalve, and may be described as an outboard-installed, bottom-loadedpacking assembly. The cartridge packing assembly 300 is similar to theprevious example packing assembly in that it facilitates repair ofexisting control valves and provides an alternate means of adjustment.In this embodiment, the packing stress is applied from in the samedirection as the process pressure, as previously described. The examplecartridge packing assembly 300 is installed in an outboard packing box380 of a control valve body 390. The cartridge packing assembly 300comprises a packing flange 328 and a retainer 355 which form a cartridgepacking box 383 consisting of two substantially concentric bores 352 and338. The first bore is a packing bore 352 formed within the packingflange 328 and is comprised of outer wall 354 terminating in a shoulder353. The second bore is a retainer bore 338 adapted to receive the outerwall 354 of the packing flange 328. The cartridge packing box 383 formsa contained volume to house a packing set 320, a stepped spacer 341 anda loading assembly 340, as described below. It should be appreciated byone of ordinary skill in the art that the stepped spacer 341 performssubstantially the same function in this present example set aspreviously described. That is, the stepped spacer 341 transmits thepacking stress from the loading assembly 340 via support of a retainerassembly 355.

Similar to the previous example packing assembly, the cartridge packingassembly 300, the retainer bore 338 terminates in a shoulder 365 tosupport the loading assembly and couple the loading assembly force tothe packing set 320. The packing set 320 and the retainer 355 areretained within the control valve body 390 by the packing flange 328 ina manner previously described with fasteners 375 that pass throughclearance holes 372 and engage an internal threaded portion 376 of thevalve body 390. The packing flange 328 also includes an annular recess393 and a flat sheet gasket 394 or similar sealing device to create aflange seal to prevent high pressure leaks past the cartridge packingassembly 320. The present example may be used as a non-adjustablearrangement shown when the pre-determined packing stress is based upon aloading force limitation defined by a controlled distance between aretainer shoulder 368 that contacts the upper surface of the valve body325; a seating surface 365 for the loading assembly 340; and aninsertion depth of a cylindrical portion 329 of the packing flange 328with respect to the upper surface of the valve body 325. The packingflange 328 may also provide an adjustment means to provide additionalpacking stress in certain new or repair, as described in detail below.

The sealing components of the example cartridge packing assembly 320 aresimilar to the previously described inboard-installed packing assembly.That is, the packing set 320 is comprised of a single seal ring 325 andtwo anti-extrusion rings 323 and 327. The materials of construction andfunction of these components are substantially similar to those previousdescribed for like components in the prior example packing sets. Thepacking assembly 320 also uses two anti-extrusion washers 332 and 333positioned on an outboard and inboard side of the packing set 320, asshown in FIG. 4.

The retainer 355 of the cartridge packing assembly 300 is formed of agenerally cylindrical shape having two concentric retainer bores. Asillustrated in FIG. 4, the retainer bore 338 is adapted to receive aportion of the packing flange 328, the loading assembly 340, and aportion of the stepped spacer 341. A second bore 370 is adapted toreceive the valve stem 315 and generally provide a clearance bore toreceive the valve stem 315 that will not abrade the surface of the valvestem 315 which may cause packing degrading and fluid leaks. One skilledin the art should appreciate that the present example packing assembly300 may also include a journal bearing (not shown) as a guide sleeve,similar to the previous example packing assembly to substantially reducethe effects of any side loads exerted by turbulent process fluids oractuator misalignment.

The example cartridge packing assembly 320 of FIG. 4 also includes anadjustment means to control the Belleville spring pre-load or packingstress within the packing assembly 320. As shown in FIG. 3, a sealedadjustment screw 391 is operatively coupled to the retainer 355 to movethe retainer 355 along an axial direction towards/away from the outboardside of the control valve body 390. It should be appreciated by one ofordinary skill in the art that the adjustment screw 391 may be sealed byvarious methods such as an o-ring 392 or the like, as shown in FIG. 3.In the present example cartridge packing assembly 300, the adjustment ofthe packing stress results from rotating the adjustment screw 391 in aclockwise or counterclockwise direction depending upon whether thepacking stress is to be increased or decreased. That is, the retainer355 may be drawn towards the outboard side of the control valve body 390to further compress the loading assembly to increase the packing stress,as desired. The example packing assembly 300 also includes an adjustmentlimiter.

The retainer 355 can travel towards the outboard side of the packingassembly until the upper surface 356 of the retainer assembly 355contacts the limiter surface 397 of the flange 328. An alternateadjustment limiter may also be arranged within the stepped spacer 341.For example, an upper portion 343 of the stepped spacer 341 isconfigured to cooperate with the flange packing bore 352 such that theupper portion may be received within the flange packing bore 352 as thepacking stress is adjusted. The stepped spacer 341 may be furtherconfigured such that a lower portion 344 may engage a packing boreshoulder 353 to limit the travel of the stepped spacer to ensure aminimum packing stress to provide an environmental seal, or may beindicative that the packing set 320 should be replaced if a sealedcannot be maintained.

While there have been shown and described what are at present consideredthe preferred embodiments of the present invention, it will be obviousto those skilled in the art that various changes and modifications maybe made therein without departing from the scope of the invention asdefined by the appended claims. For example, one skilled in the artshould appreciate that the present embodiments may also be used withpacking set that have non-V-ring style cross-sections such as die-formedribbon packing or braided rope-style packing. Although certainapparatus, methods, and articles of manufacture have been describedherein, the scope of coverage of this patent is not limited thereto. Tothe contrary, this patent covers all apparatus, methods, and articles ofmanufacture fairly falling within the scope of the appended claimseither literally or under the doctrine of equivalents.

1.-16. (canceled)
 17. A cartridge packing assembly to seal a valve stemin a control valve assembly, the cartridge packing assembly comprising:a seal assembly having a seal component to provide a fluid seal aroundthe valve stem and at least a first anti-extrusion component tosubstantially prevent extrusion of thc seal member about the valve stem;a loading assembly having a loading means to provide a predeterminedpacking stress upon the seal assembly and at least one spacer to couplethe loading means to the seal assembly; and a packing retainer adaptedto be disposed in an outboard packing box of the control valve assembly,the packing retainer defining a packing bore receiving the seal assemblyand the loading assembly wherein the packing retainer includes apredetermined length between a retainer shoulder and a loading meansseating surface to control a loading assembly force that defines thepredetermined packing stress in the control valve assembly.
 18. Thecartridge packing assembly of claim 17, wherein the loading assemblyforce provides a substantially constant, packing stress supplemental toa process packing stress resulting from a process pressure within thecontrol valve assembly.
 19. Thc cartridge packing assembly of claim 17,wherein the packing retainer provides a corrosion resistant sleeve inthe outboard packing box.
 20. The cartridge packing assembly of claim19, wherein the packing retainer is formed from a material selected fromthe group consisting of S31600, Inconel, Hastelloy, and PEEK.
 21. Thecartride packing assembly of claim 17, wherein the seal componentcomprises at least a seal ring consisting of PTFE.
 22. The cartridgepacking assembly of claim 17, wherein the first anti-extrusion componentcomprises at least one of an anti-extrusion washer or an anti-extrusionv-ring.
 23. The valve packing assembly of claim 22, wherein theanti-extrusion component comprises a material of filled-PTFE having asubstantially non-abrasive filler.
 24. The valve packing assembly ofclaim 23, wherein the substantially non-abrasive filler is molybdenumdisulfide.
 25. The valve packing assembly of claim 22, wherein theanti-extrusion component comprises a material of filled-PTFE having afiller selected from the group consisting of graphite, carbon, silica,and barium sulfate.
 26. The valve packing assembly of claim 23, whereinthe anti-extrusion component further comprises a reinforcing polymer ofPEEK.
 27. The cartridge packing assembly of claim 17, wherein theloading means comprises a stack of multiple Belleville washers.
 28. Thecartridge packing assembly of claim 17, wherein the packing retainer isretained within the control valve assembly by a flange component. 29.The cartridge packing assembly of claim 28, wherein the flange componentfurther includes an adjusting means to modify the loading assemblyforce.
 30. The cartridge packing assembly of claim 29, wherein theadjusting means is operatively coupled to the retainer.
 31. Thecartridge packing assembly of claim 29, wherein the adjusting means isoperatively coupled to a second spacer.
 32. The cartridge packingassembly of claim 17, wherein the packing retainer further comprises ajournal bearing to guide the valve stem in the control valve assembly.33.-45. (canceled)